1. Field of the Invention
This invention relates to an electrophotographic photosensitive member, and a process cartridge and an electrophotographic apparatus which have the electrophotographic photosensitive member. More particularly, it relates to an electrophotographic photosensitive member having on a cylindrical support a photosensitive layer and a protective layer in this order, which cylindrical support has an outer diameter of less than 30 mm; and a process cartridge and an electrophotographic apparatus which have such an electrophotographic photosensitive member.
2. Related Background Art
With achievement of high image quality and high-speed and high-durability image formation in recent years, organic electrophotographic photosensitive members making use of organic photoconductive materials are also required to be more improved in mechanical durability.
In recent years, electrophotographic apparatus such as printers, copying machines and facsimile machines making use of electrophotographic photosensitive members have also come into wide use in various fields, and are more severely required to provide images which are always stable even in more various environments.
Electrophotographic photosensitive members, to which electrical and mechanical external forces are directly applied, are required to have durabilities to such forces. Stated specifically, they are required to have durability to the occurrence of surface wear and scratches due to friction and durability to the deterioration of surface layer that is caused by adhesion of active substances such as ozone and nitrogen oxides generated at the time of charging.
In addition, electrophotographic photosensitive members are repeatedly put to steps of charging, exposure, development, transfer, cleaning and charge elimination. An electrostatic latent image formed upon charging and exposure is made into a toner image by the use of a toner. This toner image is further transferred to a transfer material such as paper by a transfer means, where it is not that the toner of the toner image is all transferred but that it remains partly on the surface of the photosensitive member as a transfer residual toner.
If this transfer residual toner is in a large quantity, i.e., any faulty transfer occurs, the image on the transfer material comes into an image with what is called crumbling blank areas. This not only results in lack of image uniformity but also may cause a problem that the melt adhesion of toner or filming occurs on the electrophotographic photosensitive member. To solve such a problem, it is required to improve the releasability of the surface layer of the electrophotographic photosensitive member.
To meet such requirements, it has been attempted to provide protective layers of various types. Among various attempts, protective layers composed chiefly of resins have been proposed in a large number. For example, as disclosed in Japanese Patent Application Laid-Open No. 57-30846, a protective layer is proposed which is formed of a binder resin to which a metal oxide is added as conductive particles so that its volume resistivity can be controlled.
As also disclosed in Japanese Patent Application Laid-Open No. 6-82223, it is proposed to use a curable phenolic resin as a resin for protective layers. However, in an electrophotographic photosensitive member disclosed in this publication, carbon fluoride is dispersed in its protective layer, and hence the resin of the protective layer has a low transparency to make images have a poor one-dot reproducibility.
The metal oxide is dispersed in the protective layer of an electrophotographic photosensitive member chiefly in order to control the volume resistivity of the protective layer itself to prevent residual potential from increasing in the photosensitive member as the electrophotographic process is repeated. It is known that suitable volume resistivities of protective layers for electrophotographic photosensitive members are 1010 to 1015 xcexa9xc2x7cm.
However, where the volume resistivity is within the above range, the volume resistivity of the protective layer tends to be affected by ion conduction, and hence the volume resistivity tends to undergo great changes depending on environmental changes. In particular, in the case when the metal oxide is dispersed in the protective layer, the metal oxide surface has so high water absorption properties that it has hitherto been very difficult to keep the volume resistivity of the protective layer within the above range in every environment and besides in the repetition of the electrophotographic process. Especially in an environment of high humidity, the volume resistivity may gradually lower with leaving and the active substances such as ozone and nitrogen oxides generated at the time of charging may repeatedly adhere to the surface. These may cause a decrease in volume resistivity of the electrophotographic photosensitive member surface layer and a lowering of releasability of toner from the surface layer, bringing about problems that defects such as what is called smeared images and blurred images may occur and that an insufficient image uniformity may result.
Where particles are dispersed in the protective layer as commonly done, it is preferable for the particles to have a particle diameter which is smaller than the wavelength of incident light, i.e., 0.3 xcexcm or less.
However, metal oxide particles usually tend to agglomerate in a resin solution and may uniformly be dispersed with difficulty. Even if they have once been dispersed, they tend to cause secondary agglomeration or sedimentation. Accordingly, it has been very difficult to stably produce films in which fine particles of 0.3 xcexcm or less in particle diameter are dispersed in a good state.
In addition, from the viewpoint of improving the transparency and conduction uniformity of the protective layer, it is preferable to disperse ultrafine particles having especially small particle diameter (0.1 xcexcm or less in primary particle diameter), but such ultrafine particles tend to have poorer dispersibility and dispersion stability.
In order to compensate the above disadvantage, for example, Japanese Patent Application Laid-Open No. 1-306857 discloses a protective layer to which a fluorine-atom-containing silane coupling agent, a titanate coupling agent or a compound such as C7F15NCO has been added; Japanese Patent Application Laid-Open No. 62-295066, a protective layer in a binder resin of which fine metal particles or fine metal oxide particles improved in dispersibility and moisture resistance by water-repellent treatment have been dispersed; and Japanese Patent Application Laid-Open No. 2-50167, a protective layer in a binder resin of which fine metal oxide particles surface-treated with any of a titanate coupling agent, a fluorine-atom-containing silane coupling agent and an acetoalkoxyaluminum diisopropionate have been dispersed.
An example in which a charge-transporting material having a hydroxyl group is contained in the protective layer is also disclosed in, e.g., Japanese Patent Application Laid-Open Nos. 10-228126 and 10-228127.
An example in which a phenolic resin is used as the binder resin used in the protective layer is also disclosed in, e.g., Japanese Patent Application Laid-Open No. 5-181299.
Under existing circumstances, however, even these protective layers have not achieved any durability and releasability against various impact to surface and against wear and scratching, which are high enough to be able to meet the high durability and high image quality required in recent years.
In addition, there is an increasing need for space saving, and it is driven by necessity to make small the size of the main body of an electrophotographic apparatus. Accordingly, it is necessary to manufacture electrophotographic photosensitive members adapted to the size of the main body, and it is essential to make electrophotographic photosensitive members have a small diameter.
However, in an attempt to make achievement both for manufacturing an electrophotographic photosensitive member having a protective layer with wear resistance and for making the electrophotographic photosensitive member have a small diameter, there is a very great problem.
Not coming into question so much in electrophotographic photosensitive members having a diameter employed commonly in conventional cases, as a result of making the electrophotographic photosensitive member have a small diameter, a great stress is applied to the protective layer. Loads are applied thereto from members coming into direct contact with the electrophotographic photosensitive member, such as a charging means, a developing means and a transfer means when it is mounted to the electrophotographic apparatus. This may consequently cause a problem that the protective layer comes off because of any small scratches made during processing. This problem comes more remarkable when a curable resin is used as the binder resin of the protective layer.
Moreover, because of the fact that the electrophotographic photosensitive member has a small diameter, it must be rotated in a larger number than conventional electrophotographic photosensitive members in order to reproduce images on one sheet, so that a much greater load is applied to the electrophotographic photosensitive member.
Where the protective layer is made to have a small modulus of elastic deformation in order to relax the stress, it follows that the electrophotographic photosensitive member is rotated dragging any external additives of toner which have adhered to the protective layer. This may inevitably cause deep scratches, so that the protective layer may not function as such any longer.
In addition, the internal temperature of the electrophotographic apparatus tends to rise during image reproduction, and the temperature of the electrophotographic photosensitive member also rises correspondingly to the internal temperature of the electrophotographic apparatus, so that any difference in coefficient of thermal expansion between the protective layer and the photosensitive layer may make poor the adherence between the both layers. If a load is applied to the electrophotographic photosensitive member in this state, the protective layer may inevitably lift or come off because the adherence between them stands poor.
An object of the present invention is to solve the above problems to provide an electrophotographic photosensitive member which does not cause any come-off of, or toner""s melt adhesion to, the protective layer even where the photosensitive layer and the protective layer are formed on a small-diameter cylindrical support, and has a protective layer having superior scratch resistance and wear resistance; and a process cartridge and an electrophotographic apparatus which have such an electrophotographic photosensitive member.
As a result of extensive studies, the present inventors have discovered that the above problems can be solved as long as, in an electrophotographic photosensitive member having a photosensitive layer and a protective layer on a small-diameter cylindrical support, the difference between a coefficient of thermal expansion measured from the top of the protective layer and a coefficient of thermal expansion measured after the protective layer has been removed and the modulus of elastic deformation measured from the top of the protective layer are within specific ranges.
More specifically, the present invention is an electrophotographic photosensitive member comprising a cylindrical support, and provided thereon a photosensitive layer and a protective layer in this order, which cylindrical support has an outer diameter of less than 30 mm, wherein;
the difference between a coefficient of thermal expansion (xcex11) measured from the top of the protective layer and a coefficient of thermal expansion (xcex12) measured after the protective layer has been removed, |xcex11xe2x88x92xcex12|, is more than 5.0xc3x9710xe2x88x927xc2x0 C.xe2x88x921 to less than 1.0xc3x9710xe2x88x924xc2x0 C.xe2x88x921; and
the modulus of elastic deformation We % measured from the top of the protective layer is more than 30% to less than 60%.
The present invention is also a process cartridge comprising an electrophotographic photosensitive member and at least one means selected from the group consisting of a charging means, a developing means, a transfer means and a cleaning means which are integrally supported, and being detachably mountable to the main body of an electrophotographic apparatus, wherein;
the electrophotographic photosensitive member is the electrophotographic photosensitive member described above.
The present invention is still also an electrophotographic apparatus comprising an electrophotographic photosensitive member, a charging means, an exposure means, a developing means and a transfer means, wherein;
the electrophotographic photosensitive member is the electrophotographic photosensitive member described above.